With variables you can customize many aspects of install4j. They can be used in all text fields and text properties in the install4j IDE as well as from the install4j API. The general variable syntax is

where prefix denotes the functionality scope of the variable and is one of

Text fields in the install4j IDE where you can use variables have a   variable selector next to them. In the popup menu, you first choose a variable system from the available variable types. In text properties of an installer element or a form component, you can use compiler variables, installer variables and custom localization keys, but not launcher variables.

The variable selection dialog then shows all known variables of the selected variable type.

For both compiler and installer variables install4j offers a fixed set of "system variables". These variables are prefixed with "sys.". These variables are not writable and it is discouraged to use this prefix for your own variables.

Compiler variables

Compiler variables are written as

The value of a compiler variable is a string that is known and replaced at compile time. The installer runtime or the generated launchers do not see this variable, but just the value that was substituted at runtime.

You can use compiler variables for various purposes. The most common usage of a compiler variable is the possibility to define a string in one place and use it in many other places. You can then change the string in one place instead of having to look up all its usages. An example of this is the pre-defined "sys.version" variable that contains the value of the text field where you enter the application version. Another usage for compiler variables is to override certain project settings on a per-media file basis. For example, if you want to include one directory in the distribution tree for Windows but another one for macOS, you can use a compiler variable for that directory and override it in the media file wizard. Finally, compiler variables can be overridden from the command line compiler and the ant task.

When you use a compiler variable in your project that is not a system variable, it must be defined in on the Compiler Variables tab of the General Settings step. If an unknown variable is encountered, the build will fail. You can use other variables in the value of a variable. Recursive definitions are detected and lead to a failure of the build. It is not possible to define compiler variables with the name of a system variable.

install4j provides a number of system compiler variables:

You can access environment variables on the build machine with the syntax

where "environmentVariableName" is the name of an environment variable. This only works if no compiler variable with the same name is defined on the Compiler Variables tab. This is resolved at build time, not at run time.

In order to debug problems with compiler variables, you can switch on the extra verbose output flag in the Build step. All variable replacements will be printed to the build console.

Installer variables

Installer variables are written as

The value of an installer variable is an arbitrary object that is not known at compile time. Installer variables are evaluated when requested in the installer or uninstaller. Installer variables can be predefined in the install4j IDE like compiler variables, but this is not necessary. Undefined installer variables come into existence the first time they are defined at runtime. However, it is an error to use an undefined variable. For example, if you use an installer variable in an action, you have to make sure that the installer variable is defined before the action is executed.

Installer variables are used to wire together actions, screens and form components at runtime. The user input in screens is saved to variables, which can be used in the properties of certain actions. Furthermore, variables are routinely used in condition and validation expressions. Some examples are given in the help topic on form screens. In expression/script properties, you retrieve variables by invoking

context.getVariable(String variableName)
Variable value can be set with the installer API by invoking
context.setVariable(String variableName, Object variableValue)

You can analyze the bindings of an installer variable on the "Installer Variables" tab of an installer application configuration. It will show you a list of bound variables together with all bindings. In order to document and categorize bound installer variables, you can pre-define them and set a description for them, which will be displayed in the installer variable selector in the install4j IDE.

A common scenario is the need to calculate a variable value at runtime with some custom code and use the result as the initial value of a component in a screen. To achieve this you can add a "Set a variable" action to the startup screen and set its "Variable name" property to some variable name. In contexts where a variable name is expected by install4j, you must not use the ${installer:variableName} syntax but specify variableName only. The return value of the "Script" property is written to the variable. If, for example, the variable represents the initial directory that is displayed for a customizable "Directory selection" screen, you then set the "Initial Directory" property of that screen to ${installer:variableName}. In this way you have wired an action with a screen.

Another important use of installer variables is for the locations of custom installation roots. In most cases a custom installation root contains an installer variable that is resolved at runtime. Often, one of the system installer variables that represent a "magic" folder can be used, such as the Windows system32 directory.

Installer variables can be passed to the installer or uninstaller from the command line prefixed with -V (for example -VmyVar=test). Alternatively, you can specify a property file containing installer variables with -varfile (for example -varfile myfile.prop). The variables will be String objects.

install4j provides a number of system installer variables:

Launcher variables

Launcher variables are written as

The value of a launcher variable is a string that is not known at compile time. Launcher variables are evaluated when a generated application launcher is started. Launcher variables can only be used in the VM parameters text field of the launcher wizard. No user-defined launcher variables exist, the available system launcher variables are:

I18N messages

I18N messages are written as

The value of an I18N message depends on the language that is selected for the installer. You can use this facility to localize messages in your installers if they support multiple languages. You can supply key value pairs for internationalization in the custom localization file. The variable selection dialog for I18N messages shows all system messages as well as all messages in the custom localization file for the principal language of your project.

All standard messages displayed by install4j can be referenced with this syntax as well. You can locate the key name in one of the message_*.utf8 files in the $INSTALL4J_HOME/resource/messages directory and use it anywhere in your project. The standard messages can be overwritten by your custom localization files.

Using variables your own applications

Many times there is a need in the installed applications to access user input that was made in the installer. The install4j API provides the helper class com.install4j.api.launcher.Variables to access the values of installer variables.

There are two ways that installer variables can be persisted in the installer: First, installer variables are saved to the default response file .install4j/response.varfile that is created when the installer exits or if a "Create response file" action is executed. Only response file variables are saved to that file. Please see the help topic on response files for more information. Second, selected installer variables can be saved to the Java preference store. The com.install4j.api.launcher.Variables helper class offers methods to load variables from both sources.

Saving to the Java preference store is interesting if you want to modify those variable values in your applications and save back the modified values. The Java preference store is available on a per-user basis so that it is possible to modify settings even if the user does not have write permissions for the installation directory. The com.install4j.api.launcher.Variables helper class has methods for loading and saving the entire map of installer variables that way saved by the installer. Also, it is possible to specify an arbitrary package to which the installer variables are saved, so that communication of settings between installers is made possible.

Lastly, it is useful to access compiler variables in your own applications. For example, the version number configured in the install4j IDE can be accessed in your own application through the com.install4j.api.launcher.Variables helper class.